Quote: "In order to sue you, the BBC would need to prove loss of earnings"
exactly... you make nothing, they're not loosing a penny. And unless the game is actually Dr Who themed they can't prove that it would take away potential customers for thier merchandise - especially as you need to prove that over 10,000 poeple or more are using the said program to be able to claim that it is a wise enough audience to hurt sales.
put bluntly, its only the petty as hell american companies that will do anything about the copyrights.
Just look at Bid For Power, Toei Studios own the copyrights to DBZ ... but as Funimation have the US Rights, they shut down the BFP team - Toei Studios knew about the mod ... they apparently even backed the mod, but as the rights were Funimations - sadly an online game was shut down (until they thoughtof a craft way around it)
BFP was still released, it still has the DBZ character... all funimation did was piss everyone off involved.
But quite frankly if an amature group makes a game so good that it threatens your sales then quite frankly you need better developers rather than shutting down the amatures